Category Archives: Swift

Big iOS learning classic is back again

The very well-known Stanford University’s course CS193p (Developing Applications for iOS using SwiftUI) formerly using Swift, has been broadcasted again this year.

This is the second time the curse is entirely done in SwiftUI. The course is very similar to last years’ but has some new approaches and updates that might worth repeating.

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Cocoapods Pod install – Pod update differences

How to get a clear succinct picture of these two popular actions.

Use pod install to install new pods in your project. Even if you already have a Podfile and ran pod install before; so even if you are just adding/removing pods to a project already using CocoaPods.

Use pod update [PODNAME] only when you want to update pods to a newer version.

Now, here’s the tricky part, if there’s an existing Podfile.lock that specifies the versions of all requested pods, there is no difference.

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Dependency injection

In software engineering, dependency injection is a technique in which an object receives other objects that it depends on. These other objects are called dependencies. In the typical “using” relationship the receiving object is called a client and the passed (that is, “injected“) object is called a service.

The code that passes the service to the client can be many kinds of things and is called the injector. Instead of the client specifying which service it will use, the injector tells the client what service to use. The “injection” refers to the passing of a dependency (a service) into the object (a client) that would use it.

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SOLID PROGRAMMING – LISKOV SUBSTITUTION PRINCIPLE

Substitutability is a principle in object-oriented programming stating that, in a computer program, if S is a subtype of T, then objects of type T may be replaced with objects of type S (i.e. an object of type T may be substituted with any object of a subtype S) without altering any of the desirable properties of the program (correctness, task performed, etc.). More formally, the Liskov substitution principle (LSP) is a particular definition of a subtyping relation, called (strongbehavioral subtyping, that was initially introduced by Barbara Liskov in a 1987.

The Liskov Substitution Principle is the third of Robert C. Martin’s SOLID design principles. It extends the Open/Closed principle and enables you to replace objects of a parent class with objects of a subclass without breaking the application. This requires all subclasses to behave in the same way as the parent class.

Therefore:

Functions that use pointers or references to base classes must be able to use objects of derived classes without knowing it.” – Robert C. Martin

A violation of this behaviour would imply your code is not SOLID and it may be prone to malfunctioning.

What’s new in Swift 5.0

A new version of the Swift programming language is coming: Swift 5.0. It’s slated to be released early 2019, with a fair number of changes. How does this Swift update affect practical iOS development? And who’s making these changes anyway?

In this article, we’ll walk through some of the proposed and accepted changes for Swift 5.0. We’ll also discuss how the process of making changes to the Swift language works, and why that’s relevant for iOS developers.

Version 5 of Apple’s Swift language used for iOS and MacOS application development will arrive in 2019 with ABI (application binary interface) stability in the standard Swift library a primary focus.

ABI stability is half of what is needed to support binary frameworks. The other half, module stability, will be a “stretch goal” for Swift 5 and may not make it into the release, Apple’s roadmap notes.

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iPhone Device & Screen Sizes and Resolutions +Xr

To get the screen dimensions (in points) of the current device:

Objective-C: 
CGRect screenBounds = [[UIScreen mainScreen] bounds]; 
// Macros: 
#define screen_width [ [ UIScreen mainScreen ] bounds ].size.width #define screen_height [ [ UIScreen mainScreen ] bounds ].size.height 
Swift: 
let screenBounds = UIScreen.main.bounds 
let screen_width = screenBounds.width 
let screen_height = screenBounds.height 

To get the screen scale:

Objective-C: 
CGFloat screenScale = [[UIScreen mainScreen] scale]; Swift: let screenScale = UIScreen.main.scale

Non-retina devices have a scale of 1.0. Retina devices have a scale of 2.0 or 3.0.

Some dimensions common to all screen sizes:

Status Bar
20 pts
Navigation Bar44 pts
Nav Bar/Toolbar Icon20 x 20 pts (transparent PNG)
Tab Bar49 pts
Tab Bar Icon30 x 30 pts (transparent PNGs)

Points vs. Pixels

Apple introduced retina displays starting with the iPhone 4. You don’t have to modify your code to support high-res displays; the iOS coordinate system uses points rather than pixels, so the dimensions and position in points of all UI elements remains the same across all devices.

iOS supports high resolution displays via the scale property on UIScreen, UIView, UIImage, and CALayer classes. If you load an image from a file whose name includes the @2x modifier, its scale property is set to 2.0. Similarly an image with a @3x modifier has a scale of 3.0. Otherwise the scale defaults to 1.0.

Retina Graphics

To support high-resolution graphics on devices with retina displays, you need @2x and @3x sized images:

@1x:
button.png
60 x 20
@2x:
button@2x.png
120 x 40
@3x:
button@3x.png
180 x 60

To refer to an image in your code (or in Interface Builder), just use the filename of the standard sized image. iOS will automatically detect and use the @2x or @3x version if the device supports it:

Objective-C: 
<br>imageView.image = [UIImage imageNamed: @"button.png"]; Swift: imageView.image = UIImage(named: @"button.png")